Flow detector

Description and mechanism

Flow detector can be any device capable of using reactive element in order to detect invisible Flow of Atocitera.
Most commonly spread are simple airtight tubes with the reactive element inside.
Living on Atocites, the most accessible reactive element are parts of the flying mountains themselveves for their natural ability to absorb the Flow.

Most basic detectors are then just a small amount of sand from Atocites in an airtight tube.
While in the presence of Flow, the sand from Atocites absorbs the Flow and starts floating as if weightless inside the tubes.
But more complex versions also exist. Adding bits of crystals into the tube attune the sand from Atocites with the particular element, making it react to more Flow of the same element. This way there is a use for otherwise useless bits of crystals.
Most advanced detectors use several individual tubes to detect all elements.
Detecting Corruption is much trickier because no corruption is allowed to be brought up onto Atocites.
Knowledge of Flow detectors is however very simple and common so any Raider can build themself a Corruption detector when they find something corrupted on the Ground bellow while having a tube for it.
Some parts from monsters make even better reactive elements for Flow detectors. These parts not only react to a particular Flow, but they also react with measurable intensity.

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Usage

Flow detector allows raiders to detect the presence and intensity of the Flow.
The presence of Flow can be dangerous during hunting. Abilities are much more commonly seen among monsters than among the Raiders, so this put Raiders at disadvantage when fighting inside the Flow. It is also good to know how the presence of Flow can affect certain abilities. Knowledge about its presence or absence is then a strategical advantage.
A monster that is normally perfectly safe might be a lethal threat just because the Flow is augmenting its abilities.
The Flow detector is often wielded on the wrist, sometimes even as part of a weapon. The key is accessible visibility to check the presence of the Flow.
Occasionally, the Flow detectors are used to detect the element of internal Flow of the people. Which can affect growth, moods, psychology and abilities the user can develop.
It can also detect 

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Discovery

The mountains of Atocitera had their Flow absorbing abilities since recorded history, and people were well aware of that fact.
Because of that, the Flow detectors were actually invented and used long before the Cataclysm.  The people however had no way of knowing which element the Flow in the area was aligned with as they did not have any aligned reactive element.
In ancient times, Flow detectors were used to measure if the land was blessed by the presence of Flow.
Sites and lands considered to be blessed were then preferred as building places.

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Materials

The creation of a simple Flow detector requires very few things and could be created almost entirely with things available on the Ground below.

The required materials for core functionality are:
A glass tube, box, or any other container that can be closed airtight while providing visibility on its content.
Few grams of the reactive element. Reactive elements on the Ground below are always attuned to a certain element.

The core functionality is achieved when a reactive element is sealed in a container that is airtight to prevent as much outside influence as possible.
The reactive elements will visibly react in presence of the Flow.

After the core function is achieved, additional components can be used to achieve the following.
Attaching the container to a wrist or somewhere else visible.
Connecting variously aligned detectors together to detect multiple elements within the same Flow.